Transparent and translucent samples have been analyzed by means of colorimeters or spectrophotometers which ascertain absorbance and/or transmittance at various wavelengths of the sample. Liquids and substances, which are capable of being dissolved or carried in suitable liquids, may be analyzed by passing the liquid through a cuvette which is mounted in the path of a light beam of a colorimeter. In order that analyses may be accomplished quickly, it is desirable, in the case of fluid analysis, to provide means for making continuous indications of the absorbance or transmittance at various wavelengths of light through the sample as the liquid flows through the cuvette. In the case of amino acid analysis, for example, the effluent from a liquid chromotograph instrument, where the amino acids are separated, is carried by the buffer solution into a mixing chamber or tube where a ninhydrin solution is introduced. The amino acid sample, buffer solution and ninhydrin are heated to bring out the color characteristics. The reacted effluent, carrying the separated amino acids, is then caused to flow through the cuvette of a colorimeter.
The analysis in the cuvette is accomplished by ascertaining the transmittance or absorbance at three different wavelengths such as 440 millimicrons, 570 millimicrons and 690 millimicrons. However, in the past, when making analyses of this type for the analysis of amino acids and also for similar colorimetric analyses of other liquids, it has been necessary to make separate determinations for the different wavelengths or to use separate cuvettes with separate colorimeters and this has required redundancy of apparatus greatly increasing the expense and complicating the operation of the apparatus.
It is an object of the invention to provide a colorimeter suitable for use in the analysis of amino acids which employs a single cuvette.
It is also an object to overcome the effect of base line noise or changes in base line caused by variations in flow rate, particulate matter in the cuvette, variations in metering rate, etc.
It is another object of the invention to provide absorbance signals as contrasted with transmittance signals in order to permit the signals to be ranged electrically on a recoder utilizing a simple "universal" linear scale. Thus, it is an object of the invention to avoid the necessity for employing multiple cuvette systems with long and short path lengths to achieve differing scale ranges.
A further object of the invention is to provide optical systems which permit the use of small volume cuvettes with diameters as low as 0.030 inches and relatively long path lengths through optimized collection and conservation of the shorter wavelength radiations passing from the source through the cuvette.
Other and further objects, features and advantages will become apparent as the description proceeds.